1. Field of the Invention
The present invention relates to a seatbelt retractor, and more particularly to a seatbelt retractor having a force limiter mechanism.
2. Related Technology
Recent seatbelt retractors are provided with a force limiter mechanism that reduces a load on a chest portion of an occupant by unreeling a belt while absorbing energy when a load of a set value or more is exerted on the belt (see Japanese Translation of PCT Application No. 2003-502204, for example). In the seatbelt retractor described in that document, a torsion bar is constituted by a plurality of shaft parts having different twisting torques, and by switching the plurality of shaft parts of the torsion bar using a switching device, an energy absorption load of the force limiter mechanism can be modified.
Incidentally, the switching device described in the PCT application mentioned above switches a force transmission position of the plurality of shaft parts by activating a switching member via a switch housing gas generated by a gas generator. Conventionally, to ensure that a housing portion of a switch housing for accommodating this type of gas generator does not interfere with a system cover accommodating an emergency lock mechanism or a webbing and to eliminate the need to open a hole in a frame in order to connect a connector for the gas generator, the housing portion is formed so as to bulge diagonally downward or diagonally upward along a gas flow path through which the gas flows. The gas flow path and the housing portion are formed in the switch housing by inserting sliding pieces, performing die-casting, and withdrawing the sliding pieces such that the gas flow path and the housing portion are formed rectilinearly in the parts from which the sliding pieces were withdrawn.
When the gas generator is disposed in a diagonally upward orientation, however, water and the like may infiltrate the gas generator. Further, the connector for the gas generator is preferably connected after the retractor is attached to a vehicle to prevent the connector from being pulled such that excessive force is exerted thereon during assembly, When the gas generator is to be disposed in a diagonally downward orientation, this attachment operation is difficult. Therefore, to improve ease of assembly, the housing portion is preferably formed so as to curve in a different direction to the diagonally formed gas flow path.
For example, when die-casting is performed using two sliding pieces for forming the gas flow path and the housing portion in the switch housing, one must close a die-cut hole through which the sliding piece for forming the gas flow path is withdrawn. A lid may be provided to close the die-cut hole, but this leads to an increase in the number of components and requires an attachment operation. When the switch housing is formed using lost wax casting, sand mold casting, or the like, a die-cut hole need not be provided during manufacture. However, these methods are not suitable for mass production.